A polarizing lens transmits only polarized light compared to non-polarized light using polarization phenomenon. Particularly, it blocks transmission of direct light or reflected light by diffused reflection and the like, and transmits only polarized light, thereby protecting eyes from the light source, and providing clear sight even in the state of reflected light or back light, and thus, it may secure sufficient sight at the time of automobile driving as well as sport and leisure activities, thus increasing stability.
In general, in case of a polarizing film for polarizing lens, a polymer film such as polyvinyl alcohol (PVA) and the like drawn to orient the molecules inside the film toward a specific direction exhibiting polarization property is used. In other words, it is prepared by a method of uniaxially drawing a polyvinyl alcohol film to orient the molecules inside the film in the uniaxial direction as drawn, dyeing with dichromic dye, and then, drying, or by a method of uniaxially drawing a polyvinyl alcohol film dyed with dichromic dye, and drying, and the like, wherein various colors may be realized by the combination of dichromic dyes.
Since a polyvinyl alcohol polarizing film has a property of being destroyed such as cracked or broken and the like instead of causing plastic deformation, when external force is applied (brittleness), it is very difficult to form into a circular cross section, namely, a lens shape, and it cannot be processed in a lens shape through a simple punching process and the like.
Thus, in general, a polyvinyl alcohol film for polarizing lens is prepared by forming into a lens shape in the film state, and then, removing surplus parts (trimming process). However, this method has a problem in that a large area of the polyvinyl alcohol film is lost during the forming and trimming processes.
And, when a lens is manufactured using the above-prepared polyvinyl alcohol polarizing film for polarizing lens, it is often required to separately treat with a primer so as to secure adhesion with resin for lens in order to add a plastic layer for lens and the like.
Thereafter, the primer-treated polarizing film for a polarizing lens is inserted into a glass mold including a gasket designed in a specific shape, plastic resin for lens is injected, and then, thermal polymerization is conducted to form a polarizing lens, wherein a problem is often generated in that residual stress of the polyvinyl alcohol polarizing film is relaxed by external heat to change appearance, thereby damaging optical properties or polarization properties.
In order to overcome such disadvantages, Korean Laid Open Patent Publication No. 2009-0128790 discloses a technology of laminating a triacetyl cellulose (TAC) film coated with a primer having excellent adhesion force with plastic resin for CR lens as a protection film of the polyvinyl alcohol polarizing film, and then, processing into a lens shape through punching and curving.
Meanwhile, recently, as plastic casting lens material, i.e., plastic resin for lens, polyurethane-based resin is used a lot, and since the polyurethane-based resin has relatively high refractive index and excellent lens processibility and mechanical properties, it is being rapidly spread in the market.
In case a lens is manufactured using the polyurethane-based material as plastic resin for lens, a thermal polymerization process should be passed at higher temperature for longer time than other material, and thus, when a urethane polarizing lens is manufactured, discoloration is generated in the polarizing film, rendering it difficult to control the colors, thereby significantly decreasing the final yield compared to lens of other material, and significantly increasing manufacture cost of the product.
Korean Laid Open Patent Publication No. 2014-01235599 discloses polyurethane-based plastic polarizing lens in which both sides of a polyethyleneterephthalate (PET) polarizing film are primer-treated with a coating solution containing urethane-based resin to increase adhesion with urethane-based resin. However, since the primer containing urethane-based resin is in the form of prepolymer of a compound having a hydroxyl (—OH) group and a compound having a diisocyanate group, and easily reacts with moisture, adhesion force with resin may remarkably decrease or discoloration may be generated according to surrounding environment or time elapse. Such disadvantage becomes more problematic if storage and transfer time of the polarizing film until it is prepared into a polarizing lens shape becomes longer, and becomes a fatal obstacle to the commercial application of the polarizing film.
Accordingly, there is a continued demand for studies on a polarizing film that can be applied for lens made of polyurethane-based material with excellent mechanical properties, and yet, has little damage of the optical property and polarization property of the polarizing film even with time elapse, and furthermore, can secure sufficient margin in the processing process.